Untreated bleeds in people with hemophilia A in a noninterventional study and intrapatient comparison after initiating emicizumab in HAVEN 1–3

Abstract Background Bleeding in people with hemophilia A can be life threatening, and intra‐articular bleeds can result in joint damage. Most clinical studies focus on treated bleeds, while bleeds not treated with coagulation factor(s) (untreated bleeds) are underreported. Objectives We assessed the incidence of untreated bleeds during a noninterventional study (NIS) wherein people with hemophilia A, with or without factor VIII (FVIII) inhibitors, were managed according to standard practice. Patients/Methods Using the Bleed and Medication Questionnaire, we prospectively collected data from three cohorts: Cohort A, adults/adolescents (age ≥12 years) with FVIII inhibitors; Cohort B, children (aged <12 years) with FVIII inhibitors; Cohort C, adults/adolescents without FVIII inhibitors. Untreated bleeds were analyzed for site, frequency, and etiology of bleeding and compared with those during emicizumab prophylaxis in the same individuals after transferring to a Phase III HAVEN trial. Results In the 221 participants enrolled in the NIS (Cohort A, n = 103; Cohort B, n = 24; Cohort C, n = 94), the incidence of untreated bleeds was approximately 40% of all bleeds in people with FVIII inhibitors and 26.2% in adolescents/adults without inhibitors. Approximately 70% of treated bleeds and approximately 54% of untreated bleeds in adults/adolescents were in joints. Untreated joint bleeds were less common (7.1%) in children. Overall, intra‐individual comparisons showed reduced treated/untreated bleeds following transition from standard to emicizumab prophylaxis. Conclusion A significant proportion of bleeding events are untreated in people with hemophilia A. There is a need to further understand why bleeds remain untreated and to capture such events in clinical studies.


Essentials
• In many clinical studies on people with hemophilia A, only treated bleeds are reported.
• We documented type, location, and patterns of untreated bleeds in a noninterventional study.
• We found that a significant proportion of bleeds in people with hemophilia A remain untreated.
• Incidence of untreated bleeds should be captured in clinical trials.

| INTRODUC TI ON
Hemophilia A is a bleeding disorder caused by a coagulation factor VIII (FVIII) deficiency. 1 Prophylaxis of people with hemophilia A aims to prevent bleeds; however, breakthrough bleeds can still occur in spite of treatment. [2][3][4] Annualized bleeding rate (ABR) is often used as the primary end point in clinical trials because the frequency and cumulative occurrence of bleeds is strongly correlated with long-term joint function. 3 However, data collection on bleeds is often connected with treatment in clinical studies, 5 potentially resulting in underestimated ABRs if only treated bleeds are documented, with untreated bleeds remaining unrecorded. When bleeding rates among adults/ adolescents with hemophilia A (with or without FVIII inhibitors) and children with FVIII inhibitors were investigated in an observational, noninterventional study (NIS), [6][7][8]

the Bleed and Medication
Questionnaire (BMQ), which requires patients to record bleeds independent of treatment, was implemented to facilitate prospective data collection on both untreated and treated bleeds. Data collected using the BMQ highlighted the need for ongoing treatment for bleeding events in people with hemophilia A, especially those with FVIII inhibitors. [6][7][8] However, treated bleeds only accounted for a portion of the reported bleeds. Therefore, a baseline of treated and untreated bleeds in individuals on standard FVIII or bypassing agent therapy (taken on demand or prophylactically) needs to be established to serve as a comparator for treatmentrelated outcomes with nonfactor therapies, such as emicizumab, a bispecific, humanized, monoclonal antibody, which demonstrated highly efficacious bleed protection across the HAVEN clinical study program. [9][10][11][12] The present analysis addresses the shortage of data on the type, location, and patterns of untreated bleeds among populations of people with hemophilia A of different ages and FVIII inhibitor status, providing a better understanding of the bleeds that are left untreated and could potentially contribute to long-term arthropathy and other chronic conditions associated with hemophilia A.

| Study design and participants
The NIS was a global prospective observational study collecting data on people with hemophilia A, with or without FVIII inhibitors, treated with the standard therapy at the time ( Figure 1). Full details of the design of each study cohort have been published previously. [6][7][8] Data from the NIS were used to assess the number of treated and untreated bleeds in a hemophilia A population that included children, adolescents, and adults, and to identify differences between populations with and without FVIII inhibitors. FVIII inhibitors; Cohort B, children (aged <12 years) with FVIII inhibitors; Cohort C, adults/adolescents without FVIII inhibitors. Untreated bleeds were analyzed for site, frequency, and etiology of bleeding and compared with those during emicizumab prophylaxis in the same individuals after transferring to a Phase III HAVEN trial.

Results:
In the 221 participants enrolled in the NIS (Cohort A, n = 103; Cohort B, n = 24; Cohort C, n = 94), the incidence of untreated bleeds was approximately 40% of all bleeds in people with FVIII inhibitors and 26.2% in adolescents/adults without inhibitors. Approximately 70% of treated bleeds and approximately 54% of untreated bleeds in adults/adolescents were in joints. Untreated joint bleeds were less common (7.1%) in children. Overall, intra-individual comparisons showed reduced treated/ untreated bleeds following transition from standard to emicizumab prophylaxis.
Conclusion: A significant proportion of bleeding events are untreated in people with hemophilia A. There is a need to further understand why bleeds remain untreated and to capture such events in clinical studies.

K E Y W O R D S
bleeding, factor VIII, hemophilia A, hemostasis, prophylaxis Funding information F. Hoffmann-La Roche Ltd.; Chugai Pharmaceutical Co., Ltd.

Handling Editor: Dr Cihan Ay
In brief, the NIS enrolled participants from May 2015 to March 2017 at 33 sites in 12 countries. [6][7][8] Cohort A comprised adults/ adolescents (aged 12 years or older) with congenital hemophilia A (any severity) and high-titer FVIII inhibitor history, episodic or prophylactic bypassing agent use for 6 months or more, and 6 or more or 2 or more bleeds in the past 6 months on episodic or prophylactic treatment, respectively. 7 Cohort B comprised children (aged less than 12 years) with congenital hemophilia A, high-titer FVIII inhibitor history, receiving either episodic or prophylactic bypassing agents, and 4 or more bleeds in the past 6 months (participants aged 2-11 years or older) or 2 or more bleeds in the previous 3 months (participants aged less than 2 years). 8 Cohort C comprised adults/adolescents with severe congenital hemophilia A (FVIII activity less than 1%) and no history of FVIII inhibitors, and episodic or prophylactic FVIII use for 150 days or more before enrollment. 6 Participants receiving episodic therapy must have had 5 or more bleeds in the past 6 months. Eligible participants from the NIS could subsequently enroll in one of the HAVEN trials; these were Phase III, open-label studies evaluating emicizumab prophylaxis and had eligibility criteria similar to the NIS. Full details of the designs of the HAVEN studies have been previously published. [9][10][11] Intraindividual comparisons were performed for participants who received bypassing agent or FVIII prophylaxis in the NIS and then emicizumab prophylaxis in a HAVEN study.
All studies were conducted in accordance with the International

| Data collection
Data from the NIS and HAVEN studies were used to assess the number of treated and untreated bleeds, differences in incidence between populations with and without FVIII inhibitors, and the impact of emicizumab therapy.
The BMQ was used to prospectively collect data on bleed occurrence and medication use. Information on bleeding and treatment were collected separately, enabling analysis of untreated versus treated bleeds. Using a hand-held device, participants were prompted to report perceived bleeds and/or medication use via the BMQ at least once every 7 days.
Information recorded included the type, location, and cause of bleeds; and treatment information, including the timing, dose, and purpose of treatment. Further details of the questions the participants and caregivers responded to in the BMQ are provided in Table S1.

| Data analyses
The NIS was not designed as a confirmatory study; all analyses were descriptive. [6][7][8] Participants were followed up for efficacy (bleedrelated end points) and safety from the first day of reporting until study withdrawal or completion. [6][7][8] Model-based ABR was estimated via a negative binomial regression Analysis end points included treated bleeds, all bleeds, spontaneous bleeds, and joint bleeds. Untreated bleeds were investigated as a subset F I G U R E 1 Disposition of participants in the NIS receiving episodic or prophylactic coagulation factor replacement and their transfer to the HAVEN Phase III clinical program investigating the safety and efficacy of emicizumab prophylaxis for hemophilia A. *One participant was not included in the intraindividual comparison due to a more stringent definition of what constituted prophylaxis compared with the HAVEN 2 primary analysis. 10 The total number of participants enrolled to take episodic or prophylactic treatment regimens in the NIS was fixed, as defined by the study protocol. [6][7][8] Abbreviations: FVIII, factor VIII; NIS, noninterventional study; Q2W, every 2 weeks; QW, every week of all bleeds. In the NIS and the HAVEN studies, bleeds were recorded according to the ISTH Scientific and Standardization Committee (SSC) definitions, 13 wherein bleeds of the same type and at the same anatomic location are counted as one bleed if the second bleed occurs within 72 h after stopping treatment for the first bleed (the "72-hour rule"). As the 72-hour rule would apply differently to untreated bleeds (i.e., the time period would be relative to the previous bleed rather than relative to previous treatment), it was not applied in the present analysis. As a result, each bleed was counted individually, allowing for clear identification and comparison of proportions of treated and untreated bleeds.

An event was considered a treated bleed if coagulation factors
were administered and the participant specified on the BMQ that the reason for this was to treat a bleed (Table S1); this was irrespective of the time between the bleed and the treatment. A bleed and the first treatment thereafter were considered to be linked (i.e., one treatment belonged to one bleed only), with the following exception: If multiple bleeds occurred on the same calendar day, the subsequent treatment was considered to apply for each of these multiple bleeds. Any bleed at a different location was considered a separate bleed, regardless of time from the last treatment. Untreated bleeds were any bleeds not treated with coagulation factors; "all bleeds" comprised the sum of untreated and treated bleeds.
The NIS cohorts applied the joint bleed definition of their corresponding HAVEN study, with definitions varying slightly across the three trials. Cohort A and HAVEN 1 employed the ISTH SSC definition, whereby a bleed was defined by the sensation of an aura combined with another joint bleed symptom. The definition for Cohort C and HAVEN 3 differed only in that an aura was not required. For Cohort B and HAVEN 2, a joint bleed was defined on the basis of the location of the bleed reported as being a joint; because of their age (less than 12 years), these participants were not expected to identify symptoms or the sensation of an aura. These definitions were presented in the BMQ to aid their identification (Table S1).
While bleeds attributable to a surgery/procedure were not included in the NIS primary end point of treated bleeds, 6-8 the purpose of the present study was to provide a comprehensive description of the nature of treated and untreated bleeds; therefore, all types of bleeds were included in all analyses, including those related to surgeries/ procedures. Data analyses were conducted by study statisticians and clinical pharmacologists (employed by the sponsor) who vouch for the completeness and accuracy of the statistical analyses. Data were made available to all authors, who confirm adherence to the protocol and statistical analyses plans.

| Study population
In total, 221 participants were enrolled in the NIS. Cohort A (n = 103) were monitored for a median (range) of 26.0 (4.1-69.6) weeks.
One participant withdrew for unknown reasons before reporting any bleed data and was not included in the analysis population.
Cohort B (n = 24) were monitored for 23.4 (8.7-44.1) weeks, with all participants completing the study. Cohort C (n = 94) were monitored for 29.8 (12.4-47.7) weeks. Four participants in Cohort C discontinued prematurely (two were nonadherent, one was lost to follow-up, and one died).
Participants were male, except for one female adult/adolescent participant with FVIII inhibitors ( Table 1). Approximately one third of Cohort A, and half of Cohort B had previously been treated with immune tolerance induction therapy.

| Incidence of untreated bleeds in the NIS
The incidences of treated and untreated bleeds are displayed in  (Table S2).
Approximately 50% of the untreated bleeds in the participants receiving prophylactic treatment in each cohort were followed within 24 hours by a dose of coagulation factor recorded by the participants as being for prophylaxis (Table S3).

| Untreated bleeds in the NIS: Locations and causes
For the adult/adolescent cohorts, A and C, the majority of both treated and untreated bleeds were reported in joints (54.0%-70.8%) ( Table 2). The untreated bleeds were distributed among the knee In contrast with treated muscle bleeds, the proportions of which were similar across the three cohorts (15.2%-18.0%), untreated muscle bleeds varied in frequency, with proportions of 13.5% and 32.6% for adults/adolescents with and without inhibitors, respectively, and 7.7% for the pediatric cohort ( Table 2). The predominant location for untreated bleeds in pediatric participants was "other" (85.3%); these bleeds were most commonly in the knee, mouth, back of knee, or shin. This differed from treated bleeds, of which only 33.0% were in this category.
Spontaneous bleeds accounted for 63.0% of untreated bleeds in adults/adolescents with FVIII inhibitors and 35.8% in those without FVIII inhibitors ( Figure 4A). Surgery/procedural untreated bleeds accounted for a lower proportion of untreated bleeds in adults/adolescents with FVIII inhibitors versus those without FVIII inhibitors (0.6%-0.9% vs. 15.2%).
Causes of bleeding in participants receiving episodic therapy were generally comparable with those for the overall population, except for the increased proportion of traumatic untreated bleeds in children (72.1% vs. 53.2% in the overall pediatric cohort; Figure 4B). In general, higher proportions of untreated bleeds were spontaneous among participants receiving prophylaxis (58.7%-77.3%; Figure 4C) versus those taking episodic treatment (27.9%-60.1%; Figure 4B). The proportions of bleeds that were untreated were higher in each of the HAVEN studies than in their corresponding NIS cohort ( Figure 5B). The proportions of both treated and untreated bleeds that were spontaneous decreased for participants taking emicizumab compared with previous standard prophylaxis in the NIS (Table 3).

| Intraindividual comparison of bleeds in the NIS versus following enrollment in the emicizumab interventional studies
There was a notable increase in the proportion of untreated bleeds associated with surgeries/procedures in HAVEN 3 compared with  Figure S1).

The majority of treated bleeds observed in the three cohorts
in the NIS and during HAVEN 1-3 were located in joints (49.0%-72.0%) (

| DISCUSS ION
This study quantitatively demonstrates the high proportion of bleeds that remain untreated in people with hemophilia A (26%-40% of total bleeds).
Untreated bleeds can contribute significantly to arthropathy and disease burden in people with hemophilia A. 14 Yet joint bleeds can be difficult to diagnose, and it is often hard to distinguish bleed symptoms from those of existing arthropathy. There is a need for better understanding of the types, locations, and patterns and severity of bleeds that are not treated. Collecting data on these untreated bleeds is therefore clinically important; however, many clinical studies document only treated bleeds. 5 In this study, the BMQ allowed participants to capture bleeds and bleed-related treatment independently, providing granular information on the relative incidence of treated and untreated bleeds. This allows a more comprehensive and informative evaluation of therapies.  d In addition to joint and muscle bleeds, participants in Cohort A (adults/adolescents with FVIII inhibitors) had the option to record bleed types as soft tissue bleeds, bruise/hematoma, or miscellaneous bleeds, whereas for Cohorts B (pediatrics with FVIII inhibitors) and C (adults/adolescents without FVIII inhibitors), these additional categories were substituted by the bleed type "other." This was as a result of a change in the BMQ used. e Bleeds in joint locations such as the knee, ankle or elbow were occasionally reported under the bleed type "other," for example, when the bleed was around the joint (such as bruises or hematomas).
FVIII inhibitors remains unknown but could be related to a perceived lack of efficacy or unpredictability of bypassing agents, treatment burden, or reduced access to treatment. [15][16][17][18][19] In adults with prior immune tolerance induction therapy, however, there was a lower ABR for un- The NIS and HAVEN 1-3 studies were limited by the BMQ relying on patient reporting of bleeds, which could result in both under-/ overreporting of events and a lack of interindividual standardization.
Additionally, the specific location of bleeds outside of joints and muscles were classified differently for the cohorts, meaning that these data could not be compared between groups. The finding that    In addition to joint and muscle bleeds, participants in Cohort A (adults/adolescents with FVIII inhibitors) had the option to record bleed types as soft tissue bleeds, bruise/hematoma, or miscellaneous bleeds, whereas for Cohorts B (pediatrics with FVIII inhibitors) and C (adults/adolescents without FVIII inhibitors), these additional categories were substituted by the bleed type "other." This was as a result of a change in the BMQ used.
e Bleeds in joint locations such as the knee, ankle, or elbow were occasionally reported under the bleed type "other," for example, when the bleed was around the joint (such as bruises or hematomas). reason(s) for not treating bleeds were not investigated, limiting conclusions regarding behaviors influencing bleed treatment. The intraindividual comparison, however, offered a robust design controlling for participant-related confounders in an otherwise descriptive study, which is a strength of this analysis.

| CON CLUS IONS
In conclusion, a significant proportion of subjectively perceived bleeds in people with hemophilia A remain untreated, suggesting that the full burden of the disease is not adequately captured in many clinical studies. The decision to treat a bleed or not is complex and may be influenced by patient-specific factors such as age and the presence of an inhibitor, as well as bleed and treat-

FU N D I N G I N FO R M ATI O N
The study was funded by F. Hoffmann-La Roche Ltd and Chugai Pharmaceutical Co., Ltd.